Electrical heater terminal and connector seals and methods of making the same



Dec. 3, 1963 J. VAN INTHOUDT ELECTRICAL HEATER TERMINAL AND CONNECTOR SEALS AND METHODS OF MAKING THE SAME Filed on. e. 1960 United States Patent ()fi :"ice

3,113,284 Patented Dec. 3, 1%63 3,113 284 ELECTRICAL HEATER TERMINAL AND CONNEC- g SEALS AND METHQDS OF MAKING THE Joh Inthoudt, Winter Park, Fla., assignor to Cutler- Hammer, Inc-, Milwaukee, Wis, a corporation of Delaware Filed Oct. 6, 1960, Ser. No. 61,014 9 Claims. (Cl. 338-274) This invention relates to electrical heaters and more particularly to seals for electrical heater connectors and terminals and methods of making the same.

While not limited thereto, the invention is especially applicable to sealing the terminals and connectors of tubular heaters.

An object of the invention is to provide improved terminal and connector seals for electrical heaters.

A more specific object of the invention is to provide improved heat resistant and water tight seals for electrical terminals and connectors of tubular heaters.

Another object of the invention is to provide improved methods for making electrical heater terminal and connector seals.

Another object of the invention is to provide improved methods of making heat resistant and water tight terminal and connector seals for tubular heaters.

In accordance with the invention, there are provided three modifications of tubular heater seals and methods for making the same. In a first modification, an insulated conductor is electrically connected to a heater terminal, preferably by crimping a conductive metal sleeve around the terminal and the strands of the conductor. A long epoxy sleeve is telescoped partially over the end of the heater sheath. The sleeve is filled with liquid epoxy to cover the connector, an insulating washer is inserted to close the end of the sleeve around the conductor and the liquid epoxy is cured at room temperature. In a second modification, a short epoxy sleeve is telescoped partially over the end of the heater sheath so that the terminal extends beyond such sleeve, the sleeve is filled with liquid epoxy and cured at room temperature. In a third modification, liquid epoxy is applied to the end of the heater, an apertured epoxy member is slid over the terminal against the end of the heater and the liquid epoxy is cured at room temperature whereby the latter seals such member to the end of the heater.

The aforementioned and other objects of the invention and the manner of obtaining them will best be understood by reference to the following detailed description of three modifications of tubular heater seals and methods for making the same taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a longitudinal sectional view of one embodiment of a seal surrounding an electrical connector which connects a heater terminal to an electrical conductor constructed in accordance with the invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a longitudinal sectional view of a modified seal which seals the end of a heater around a projecting terminal;

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 3;

FIG. 5 is a longitudinal sectional view of another modification of a seal which seals the end of a heater around a projecting terminal; and

FIG. 6 is a cross-sectional view taken along line 66 of FIG. 5.

Referring to FIGS. 1 and 2, there is shown an end portion of a tubular heater having a helical heater element or coil 2 of resistance wire enclosed within a metallic outer sheath 4 and being insulated therein by compacted heat conducting electrical insulating material 6 such as periclase, magnesium oxide powder or the like. An electrical terminal 8 is mechanically and electrically connected to heater coil 2 within the sheath and extends beyond the end of the heater. A flexible electrical conductor 10 of the insulated and stranded type or the like is connected to terminal 8. For this purpose, the insulation is removed from an end portion of conductor 10 to expose the conducting strands 19a and the latter are mechanically and electrically connected to terminal 8 by a metallic conducting sleeve 12 which is crimped therearound. A relatively long insulating sleeve 14 of solid epoxy resin having an internal diameter slightly larger than the external diameter of sheath 4 is partially overlapped around the end of the latter so as to surround the connector iacluding sleeve 12 and also to extend over a portion of the insulation of conductor 10. Sleeve 14 is filled with liquid epoxy resin 16 to embed the connector and an insulating washer 18 is inserted in the end of sleeve 14 around the insulated portion of conductorli). The liquid epoxy solidifies when cured at ambient temperature and adheres to the contiguous parts and seals the end of the heater between sheath 4 and terminal 8. The liquid epoxy also embeds and seals the connector between terminal 8 and conductor 10. Moreover, the liquid epoxy flows between sheath 4 and sleeve 14 and thereby rigidly secures sleeve 14 to sheath 4 and secures washer 18 to sleeve 14 whereby the structure provides a high heat resistant and water tight seal between sheath 4 and the insulation of conductor 10 and provides a mechanically strong connection for conductor 10.

The method of making the connector and seal shown in FIGS. 1 and 2 comprises electrically connecting a flexible conductor to the terminal of a tubular heater, assembling as by sliding or telescoping one end of a relatively long solid epoxy resin sleeve partially over the end of the heater sheath so that the other end of such epoxy sleeve extends beyond the connection of the terminal and conductor, filling such sleeve with liquid epoxy resin, inserting an insulating washer to close such other end of the sleeve, and curing the seal at ambient temperature approximately twenty-four hours to rigidly secure and seal the conductor to the heater sheath.

In the modification shown in FIGS. 3 and 4, the parts of the heater including heater coil 2, sheath 4, compacted insulating powder 6 and terminal 8 are similar to those in FIGS. 1 and 2 and have been given like reference characters. The seal in FIGS. 3 and 4 comprises a relatively short insulating sleeve 30 of solid epoxy resin slid about half-way of its length over the end of sheath 4 so that terminal 8 extends beyond sleeve 3%. The cavity within sleeve 30 around a portion of terminal 8 is filled with liquid epoxy resin 32 which is allowed to harden when cured at ambient temperature. Sleeve 30 has an internal diameter slightly larger than the external diameter of sheath 4 so that liquid epoxy flows therebetween. Liquid epoxy 32 when hardened, rigidly secures sleeve 34 to sheath 4 and seals the end of the heater between sheath 4 and terminal 8.

The method of making the seal shown in FIGS. 3 and 4- comprises assembling asby sliding or telescoping a relatively shorter solid epoxy resin sleeve substantially half-way of its length over one end of a tubular heater sheath so that the heater terminal extends through and beyond the other end of such sleeve, filling such sleeve with liquid epoxy resin and curing the same at ambient temperature approximately twenty-four hours to rigidly secure and the seal the terminal to the heater sheath.

In'the modification shown in FIGS. 5 and 6, the parts of the heater including heater coil 2, sheath 4, compacted insulating powder 6 and terminal 8 are similar to those in FIGS. 1-2 and 3-4 and have been given like reference numerals. The seal in FIGS. 5 and 6 comprises liquid epoxy resin 5% applied to the end of the tubular heater and a solid epoxy resin member or sleeve 52 is slid over terminal 8 against the end of the heater. Sleeve 52 has a hole therethrough large enough to receive terminal 8 and to permit liquid epoxy resin to flow between terminal 8 and sleeve 52. Terminal 8 extends beyond sleeve 50 to provide for an electrical connection. Sleeve 52 has an external diameter substantially equal to or slightly smaller than the internal diameter of sheath 4 to allow liquid epoxy to flow between sheath 4 and sleeve 52 thereby to seal sheath 4 to terminal 8 when Sleeve 52 is pressed against the end of the heater.

The method of making the seal shown in FIGS. 5 and 6 comprises applying liquid epoxy resin to the end of a tubular heater and sliding a relatively thick solid epoxy sleeve on the terminal and against the end of the heater whereby the liquid epoxy flows between the terminal and sleeve and between the sleeve and sheath to seal the terminal to the sheath.

The liquid and solid epoxy employed in the aforementioned seals is characterized by high temperature heat resistance, high moisture resistance and high mechanical strength.

The solidified filler 16 in FIG. 1, solidified filler 32 in FIG. 3 and solidified sealer St) in FIG. 5 each consists of a liquid epoxy resin which is cured or allowed to harden at ambient temperature. Epoxy resins of this type are available in two parts consisting of a base agent and a hardener which are mixed in predetermined portions before use. One type of epoxy resin which can be cured at ambient temperature and which is Well adapted for use in the invention is available commercially and known as Helix Bonding Agent R-823. It is characterized by no evaporation during curing and no shrinkage. It is inert to acids, alkalies, corrosive salt solutions, petroleum solvents, lubricating oils, alcohol, acetones and the like. The preformed sleeves 14, 30 and 52 in FIGS. 1, 3 and 5, respectively, are solid members of epoxy type resin and are available in tube form which may be cut to desired lengths. These sleeves may be made of the same resin or compound that is used for the aforementioned filling or sealing. One type of stock material from which these sleeves may be made is known as Resdel epoxy tubing and is commercially available. An advantage of using epoxy sleeves preferably of the same material as the liquid fillter or sealer is that it provides an excellent bond with the liquid epoxy. Due to the high temperature heat resistance, high moisture resistance and high mechanical strength heretofore described, the invention affords effective seals and eliminates the breakage encountered with ceramics and other materials during production and during rough handling and vibration encountered in use. Moreover, the invention affords efiicient and economical seals particularly characterized by the ease with which they can be made.

I claim:

1. In an electrical heater of the tubular type having a tubular sheath provided with an open end, a resistance conductor within said sheath, a terminal extending through and beyond said open end, and electrically insulating heat conducting material within said sheath for insulating said conductor and said terminal from said sheath, the improvement comprising a heat and moisture resistant seal on the end of said heater, said seal comprising a solid epoxy member on the end of said sheath and solidified liquid epoxy securing said member to the end of said sheath to seal the opening in the end of said sheath.

2. The invention defined in claim 1, wherein said solid epoxy member comprises a sleeve on the end of said sheath, and said solidified liquid epoxy is disposed between said sleeve and said terminal and between said sleeve and said sheath to rigidly secure said sleeve to the heater and to seal the terminal to the sheath.

3. The invention defined in claim 2, wherein said sleeve at one end surrounds the end portion of said sheath, and said solidified liquid epoxy fills the space around said terminal within said sleeve and the small space around the end of said sheath within said sleeve.

4. The invention defined in claim 2, wherein said sleeve surrounds a portion of said terminal immediately adjacent the end of the heater, one end of said sleeve abutting the insulating material within said sheath, and said solidified liquid epoxy fills the small space between said terminal and said sleeve and the space between the abutting end of said sleeve and said insulating material and sealing said sleeve to said sheath.

5. The invention defined in claim 2, together with means connecting an insulated conductor to said terminal, and wherein said sleeve at one end surrounds the end portion of said sheath, the other end of said sleeve extending beyond said connecting means, and said solidified liquid epoxy fills said sleeve to embed said connecting means.

6. The invention defined in claim 5, together with an insulating washer in said other end of said sleeve closing the space between said sleeve and the insulation of said conductor.

7. A method of making a connector seal for a tubular heater of the type having a tubular sheath provided with an open end, a resistance conductor within said sheath, a terminal extending from said resistance conductor through and beyond the end of said sheath, and heat conducting material compacted within said sheath for electrically insulating said resistance conductor from said sheath, comprising the steps of connecting an insulated electrical conductor at one end to said terminal, assembling a solid epoxy sleeve to surround at one end the open end of said sheath and extending at the other end beyond said connection to surround a portion of the insulated conductor, filling said sleeve with liquid epoxy whereby some of said liquid epoxy flows in the small space between the ends of said sheath and said sleeve, inserting an insulating washer in the other end of said sleeve to close the space around the insulation of said insulated conductor within said sleeve, and curing said liquid epoxy at ambient temperature for a predetermined time interval whereby said liquid epoxy solidifies to rigidly secure the contiguous parts to one another and to seal said insulated conductor to said sheath.

8. A method of making a seal for a tubular heater of the type having a tubular sheath provided with an open end, a resistance conductor within said sheath, a terminal extending from said resistance conductor through and beyond the open end of said sheath, and heat conducting material compacted within said sheath for electrically insulating said resistance conductor from said sheath, comprising the steps of assembling a solid epoxy sleeve to surround at one end the open end of said sheath and extending around a portion of said terminal short of the extended end thereof, filling said sleeve with liquid epoxy whereby some of said liquid epoxy flows in the small space between the ends of said sleeve and sheath, and curing said liquid epoxy at ambient temperature for a predetermined time interval whereby said liquid epoxy solidifies to rigidly secure said sleeve to said sheath and said terminal and to seal the open end of said sheath.

9-. A method of making a seal for a tubular heater of the type having a tubular sheath provided with an open end, a resistance conductor within said sheath, a terminal extending from said resistance conductor through and beyond the open end of said sheath, and heat conducting material compacted within said sheath for electrically insulating said resistance conductor from said sheath, comprising the steps of applying liquid epoxy to the open end of said sheath to cover said compacted insulating material, assembling a solid epoxy sleeve on said terminal to surround a portion of said terminal adjacent the end of the heater and pressing said sleeve against said compacted insulating material whereby some of said liquid epoxy flows in the small space between said sleeve and 5 said terminal and between said sleeve and said end of said sheath, and curing said liquid epoxy at ambient temperature for a predetermined time interval whereby said liquid epoxy solidifies to rigidly secure said sleeve to said sheath and to seal the space between said terminal and 10 said sheath.

References Cited in the file of this patent UNITED STATES PATENTS Abbott a- Sept. 8, 1936 Charbonneau et a1 Nov. 29, 1949 Schrotter et al July 23, 1957 Mairs Nov. 25, 1958 Robinson et a1 Sept. 15, 19 59 FOREIGN PATENTS Great Britain May 27, 1959 

1. IN AN ELECTRICAL HEATER OF THE TUBULAR TYPE HAVING A TUBULAR SHEATH PROVIDED WITH AN OPEN END, A RESISTANCE CONDUCTOR WITHIN SAID SHEATH, A TERMINAL EXTENDING THROUGH AND BEYOND SAID OPEN END, AND ELECTRICALLY INSULATING HEAT CONDUCTING MATERIAL WITHIN SAID SHEATH FOR INSULTAING SAID CONDUCTOR AND SAID TERMINAL FROM SAID SHEATH, THE IMPROVEMENT COMPRISING A HEAT AND MOISTURE RESISTANT SEAL ONTHE END OF SAID HEATER, SAID SEAL COMPRISING A SOLID EPOXY MEMBER ON THE END OF SAID SHEATH AND SOLIFIFIED LIQUID EPOXY SECURING SAID MEMBER TO THE END OF SAID SHEATH TO SEAL THE OPENING IN THE END OF SAID SHEATH. 